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A neutral protease with angiotensin I-forming activity which could readily be separated from acid proteases and plasma and renal renin was obtained from extracts of dog brain. This enzyme has an apparent mol wt of 40,000 by Sephadex chromatography. On chromatofocusing, it displays isoelectric points of 7.92, 7.73, and 7.42, and thus, it is a basic protein, in contrast to either renal or plasma renin which are acidic proteins. This brain enzyme does not react with antibodies specific for dog kidney renin. Since the brain enzyme forms angiotensin I from renin substrate at neutral pH, yet can be separated from and has isoelectric points different from renal renin, it is an isoenzyme of the kidney counterpart. The majority of the renin-like activity of dog brain is due to this isoenzyme. (Endocrinology 114: 2210, 1984)

Results are presented of a comparative study of several methods for detection of ketone bodies in urine involving nearly 10,000 tests on urines containing no ketones, naturally occurring ketones, and added acetoacetate. Acetest (a tablet nitroprusside test) and Ketostix (a strip nitroprusside test) are more specific and accurate, and have the proper sensitivity in comparison with test tube Rothera nitroprusside modifications or the ferric chloride test. Both the tablet and strip are also satisfactory for detection of ketones and serum or plasma. The tablet test may be used with whole blood for detection of ketonemia.

A series of lysophosphatidylethanolamine analogs containing saturated and methylene-interrupted cis-olefinic fatty chains was synthesized by phosphorylation and phosphonylation of respective fatty alcohols. Arachidonyl- and linolenylphosphorylethanolamines (12, 13), arachidonyl (2-phthalimidoethyl)phosphonate (17), and arachidonyl (2-aminoethyl)phosphonate (18) were found to be effective inhibitors of the renin-renin substrate reaction in vitro; lysophosphatidylethanolamine analogs 14-16 of lesser unsaturation were either weakly active or inactive. In a preliminary study, intramuscular administration of 25 mg/kg/day of arachidonyl (2-aminoethyl)phosphonate (18) to the hypertensive rat caused pronounced reduction (50 mm) in blood pressure within 3 days; upon continued dosage (15 mg/kg/day) of 18 for an additional 4 days, plasma renin activity was found to be 16 ng/0.1 ml/15 hr as compared with 69 ng/0.1 ml/15 hr before initial drug administration. Arachidonic acid (3), arachidonyl alcohol (8), and several corresponding tetraenoid ester, amide, mesylate, and glyceryl ether derivatives (4-7, 10, 11), that are not phosphate or phosphonate esters, were found to exhibit negligible or modest inhibition of renin activity in vitro.

[1-N-Methylisoasparagine,8-isoleucine]- (I), [1-sarcosine,4-N-methyltyrosine,8-isoleucine]- (II), [1-sarcosine,5-N-methylisoleucine,8-isoleucine]- (III), [1-sarcosine,8-N-methylisoleucine]- (IV), [1-sarcosine8k-N-methylisoleucine,8-N-methylisoleucine]- (V), [1-sarcosine,8-O-methylthreonine]- (VI), [1-sarcosine,8-methionine]- (VII), and [1-sarcosine,8-serine]angiotensin II (VIII), synthesized by Merrifield's solid-phase procedure, possess respectively 0.8, 0.3, 0.5, 1.0, 0.0, 0.5, 3.7, and 0.7% pressor activity of angiotensin II (vagotomized, ganglion-blocked rats). They caused an initial rise in blood pressure (30 min of infusion, 250 ng/kg/min in vagotomized, ganglion-blocked rats) of 16.57, 9.80, 22.80, 32.00, 7.00, 15.06, 32.50, and 11.42 mmHg and showed secretory activity (isolated cat adrenal medulla) of 1.0, 0.1, 0.01, 0.1, less than 0.01, 0.1, less than 0.01, and 0.05% of angiotensin II. On isolated organs pA2 values (rabbit aortic strips) of 8.74, 7.44, 7.64, 7.85, 7.89, 8.76, 8.63, and 8.08, and pA2 values (cat adrenal medulla of 8.16, 9.16, 9.31, 8.00, 8.00, 7.00, 9.16, and 9.33 were obtained. Dose ratios (ratio of ED20 of angiotensin II during infusion of the antagonist and before infusion of the antagonist) in vagotomized, ganglion-blocked rats, infused at 250 ng/kg/min, were 33.43, 2.14, 3.26, 2.99, 0.62, 62.52, incalculable, and 11.15, respectively. The results obtained suggest that (a) analogs I and VI are potent antagonists of the pressor response of angiotensin II in normal rat, VI being the most potent antagonist thus far synthesized; (b) replacement of position 4 (Tyr) with MeTyr or position 5 and/or 8 (Ile) with Melle in [1-sarcosine,8-isoleucine]angiotensin II reduced the antagonist activity of this peptide (rabbit aortic strips and rats), indicating that steric hindrance imposed due to N-methylation in positions 4, 5, or 8 was not favorable in eliminating the initial pressor activity or prolonging the duration of action of [Sar1, Ile8]angiotensin II without reducing its antagonistic properties; (c) except II, none of the analogs showed any enhanced duration of action, suggesting that N-methylation in positions 5 or 8 did not afford protection against proteolytic enzymes; and (d) perfusion studies in cat adrenals indicated that all of these analogs are only very weak secretagogues. With the exception of [Sar1,Thr(ObetaMe)8]angiotensin II, which gave lower antagonistic properties, all other analogs had either similar antagonistic properties or were better antagonists in adrenal medulla than in smooth muscle.

Male Sprague-Dawley rats were maintained on either a normal or low-sodium diet for 5 weeks to examine whether dietary sodium restriction alters angiotensin II (Ang II) receptors. The receptor sites in the hypothalamus-thalamus-septum (H-T-S) region of the brain, the adrenal glands and bladder visceral smooth muscle were measured by saturation isotherm binding assays using 125I-Ang II. Compared to control rats, the low-sodium diet group showed a smaller weight gain, reduced water intake, elevated hematocrit, and decreased urinary sodium concentration. In addition, sodium-depleted rats had a 10-fold elevation in plasma renin activity. However, neither binding affinity of 125I-Ang II to the brain H-T-S region nor its density was significantly different between the two groups. In contrast, both the 125I-Ang II binding density and dissociation constant in the adrenal gland were significantly elevated, while the binding density of 125-I-Ang II in the bladder smooth muscle was significantly decreased in the sodium-restricted group. These results suggest that dietary sodium depletion does not alter Ang II receptors in the rat brain areas wherein Ang II exerts the majority of its central actions.

Malonic acid has been isolated in crystalline form from flue-cured tobacco. It was also found in cured burley and Turkish tobaccos. Its concentration in green plants increased throughout the growing season.